1. Field of the Invention
The present invention relates generally to sliding sleeve cementing tools constructed for placement in a well casing, and more particularly to an improved stage cementing packer collar used for cementing casing in oil and gas wells.
2. Description of the Prior Art
In the drilling of deep wells, it is often desirable to cement the casing in the well bore in separate stages, beginning at the bottom of the well and working upward. Cementing the casing in separate stages assures less contamination throughout the zones to be cemented and reduces the possibility of lost circulation due to excessive hydrostatic pressure.
This process is achieved by placing cementing tools, which are primarily valved ports, in the casing or between joints of casing at one or more locations in the well bore, flowing cement through the bottom of the casing, up the annulus to the lowest cementing tool, closing off the bottom, opening the cementing tool, and then flowing cement through the cementing tool up the annulus to the next upper stage and repeating this process until all stages of the well are cemented.
Cementing tools used for multi-stage cementing usually have two internal sleeves, both of which are usually shear-pinned initially in an upper position, closing the cementing ports in the tool. To open the cementing ports a plug is dropped or displaced down the casing and seated on the lower sleeve. Fluid pressure is then increased in the casing until sufficient force is developed on the plug and sleeve to shear the shear pins and move the lower sleeve to the position uncovering the cementing ports. Cement is then pumped down the casing and out the ports into the annulus. When the predetermined desired amount of cement has been displaced into the annulus another plug is placed in the casing behind the cement and displaced down the casing to seat on the upper sleeve. The pressure is increased on the second plug until the shear pins holding it are severed and the upper sleeve is moved down to close the cementing ports, thereby terminating that particular stage of the cement job.
Multistage cementing tools may also include a packet element for sealing the annular space between the casing, which the cementing tool is a part of, and the borehole or between the casing and another string of casing. Multistage cementing tools containing a packer element are commonly referred to as stage cementing packer collars. The packer element of a stage cementing packer is designed to support the cement displaced through the cementing ports of the stage cementing packer while protecting formations below the packer collar from the hydrostatic pressure of the cement. In addition, the packer element is designed to seal the annular space against upward migration of fluids from formations beneath the packer collar.
The present invention relates to an improved stage cementing packer collar. The improved stage cementing packer collar of the present invention has several improvements over previous stage cementing packer collars. These improvements include: (1) shorter length; (2) a single piece housing as opposed to a two or three piece housing with welds; (3) the housing has a smaller outer diameter allowing the use of thicker-walled packer elements; (4) an option of opening the packer collar with a plug or with internal casing pressure as opposed to a plug only; (5) a smooth bore through the internal diameter of the housing after the packer collar has been drilled out; and (6) no internal closing sleeve.
The shorter, more compact stage cementing packer collar of the present invention is easier to handle and make-up into the casing string than prior art stage cementing packer collars. The single piece housing increases the structural integrity of the housing over prior art housings that are welded together. The use of thicker-walled packer elements allows a given size stage cementing packer collar of the present invention to seal a larger annular space than the same size prior art tool. In other words, a thicker packer element will seal a larger annular space than a thinner packer element.
The cementing ports in the cementing tool of the present invention may be opened by internal casing pressure alone or in conjunction with a plug. Opening the cementing ports with casing pressure only saves valuable rig time in the operation of the tool. At the same time, the capability of opening the cementing ports using the conventional plug method serves as a valuable back up system. As a result, the present invention offers a system that is operationally faster and more reliable than conventional stage cementing packer collars.
The cementing tool of the present invention has an external closing sleeve for closing the cementing ports after the cementing job is completed. As a result, a smoother bore through the internal diameter of the housing remains after drill out of the packer collar. This facilitates the subsequent running of tools through the packer collar and reduces the likelihood of tool hangup inside the packer collar, which is a problem with prior art packer collars.
The present invention, while new in design, is based on the design of the ES Cementer, a stage cementing tool manufactured by Halliburton Services. The ES Cementer is generally described in U.S. Pat. No. 5,038,862 to Richard L. Giroux and John T. Brandell, which is incorporated herein by reference. The similarity of design reduces the manufacturing costs of the present invention by using several of the same parts used in the ES Cementer. The major differences between the present invention and the ES Cementer are that the present invention has (1) a longer housing to accommodate the setting sleeve and packer element; (2) an external setting sleeve to compress the packer element; and (3) a packer element for sealing the annulus between the casing and well bore or between the casing and another string of casing.